Optical comparator



Jan. 21, 1958 PTJ. BENDT 2,820,298.

OPTICAL COMPARATOR Filed Feb. 2, 1953 4 Sheets-Sheet 1 Gtforneg Jan. zi, 195s P. J. BENDT f 2,820,298'

OPTICAL COMPARATOR Filed Feb. 2, 1953 4 Sheets-Sheet 5 nventor Jan. 21, 195s P. J. ENDf 2,820,298

v OPTICAL COMPARATOR Filed Feb. 2, 1953 4 Sheets-Shee; 4

(Ittomeg j optically., dat surface ithereonianovastone vof' Sai bersiis displacedhy an`v object-to, be measuredrsal oPrIcAL coMPARAroR Philip J. Bendt Detroit, Mich., assgnor to General Motors Corporation, Detroit, Mich., acorporation of Delaware Application'. February 2,. 1953,` Serial. No". 334,533- zo Claims. (C1. 3,3-149) fringes present in a light interference pattern-l formedA he- 2 tween ay pairV of" optically liat'A surfaces.

One of the most accurate methodsl of lineal measurementi employs a light` interference pattern which is created between a pair of optically at surfaces. In the past, it hasbeen= the practice toposition atransparent member havingan 'optically atsurface thereon so that thesurface simultaneously engages the top'ofa' standardl of known size andthe object` to bem'easured.' When a' source of monochromatic light illuminates therr 1embe1 ",va` pattern ofA so-called Newtonianlfringes' willl be; icfzrrnedV as a result of the light'interferencef that'is created` in the air wedgebetweenn the top ofl the standard; andthe opticallyflat surface; The spacing of the fringes" isf a` function of the angle of theA air wedge. Therefore, by observingthe number offringeswithin a specifieddistance itis`p'ossible by meansof trigonometryto determine the"relative;l difference between the standard of known sizeandthe object of unknown size: Although'thismetlodprovides an accurate? comparison; the boundaries' oftlie` bright and dark fringes arenot'well defined and, a's a` result, it is'very diflicultA to obtain an accurate measurement ofi the precise location of thefringes: Moreover; it isl'very diliicult to control the sensitivityof i this'r'nethodl'- of measurement;

lIt, is proposed toprovide an opticalfcomparatorjfor comparingthe size or" one. object with" the size offalf standard of knownv dimension by, ObservingI the movement of a light interference pattern created l `etween,a pairof members havingyoptically, flat 'surfacesthereon Onefof the members may be mountedon a stationaryzfrv'ame while the othermember. may.- be mounted on a `lever so that the optically atisurfaces are adjacent vand directly opposed to each other. The inner endof the lever may be supported by a hinge rigidly mounted oni the frame and lhavinga xed `axis .of rotation while, the outer, end

Y ofthe,1ever is adapted to.-engage,the.s tandard or object under comparison.- Moving .th'e;.oute'r-..end.'of"the lever a distance.. corresponding, to :the .difference yin N'the size of ther. object. .andthe standard willcause:4 the interference patterns. -to move i a` distance` indicating. wthisadilerence 4in size. In order; to allow the opticalcomparator .to measure* 'I objects of; lvaryingzsizles; it-.is `alsotproposedfto.support the object or .standard under comparisonon a -worksurface whichfrnayy be. moved-iwith..respect :tothe-cardstof/the hinge;supporting-the.lever;.

It-. i s.= further. proposedqto. provideian-optic:alcomparator n wherei ,a member havingganoptilly.atsurfaceftheremounted .adjacent.. a. second.. member,- ha-VIQBaf-n ber will pivot about an'iaxis" whichwwill cause tlieyhlvew` ICC tenian fringes formed between the optically l'ft surljaces to' appear? to rotate. rl`his he accio` pliehel Yby placing 'the axis of rotation of the"k of the surfaces. Moreover, it' is also prop p vide an optical comparator in whichv the sensitivity thereof can readily be increased or decreased.l

In the drawings:

Figure l is a diagrammatic viewV perspective ofthe component parts of a comparator embodying the present invention. l n I Figur-e 2 is a vsclieinaii'.: view of die* wir weegt# which isf tormedbetween the` adjacent optic ly liateu a'ces.

Figure 3i-s af seiremaii view shew g die ang* disposition of the` Newtonian fringes ,comprising the literference pattern which isv formed between the optically hat surfaces; f

Figur'e4 is an elevationalview of the' optical "nibers showing the' inclined' relationship of the optically' liat surfaces thereon. y Figure 5 is" a front elevationaly Viewl of embodyingthe present'v invention; a portiontl'ereof being broken away to more clearly show the'l YFigure 6 is a side elevational viewer thefgiiip'arfator sli'ow Figure 5,.a portion th;'eieoffvbeingl brokenaway.

siaiitiauy' niig die plane' offline tif-s.. cfm Biggie v l supporting structure 22 which-'mayfcomprise abas'eZS having a-substantially vertical pillar 24 o'nxone'ehdfand afmountinggmemberfZ on the'othe'r end.:` The'mounting member26- is contained in' an-*enclosure 30 Yandsnpp'orts a pairl ot'- optical members-'32 and 34; These-*members are verticallyspacedA from each other and hveoptic'lly at vsurfaces 36 f and 38 whichare adjacent land-#directly opposed'.w Thus when theyfareilluminated''byia'sliitable larnp40;T an interference pattern '42' will" vbe-"created therebetweeni Ananvilforelongated ar'm'44 may. be slidablymount'ed onthe pillar.- The arm44 issubstantallyfhorizoitzil"and extends` towardvthe enclosure The-end off tlie"a `1 "m 44 nearest "the enclosure 30 may be "providedI with af work surface 48' that is adaptedtosupp'orttheobjectSfunder comparison.V To reduce the possibilityb error'the work sirable to provide locking 'means such asia thum screw sz'for securing the ani/i144 iiipesiiieiiioiiihepiniizii. To facilitate 'movement ofthe anvil 44,""as e;

one end thereof seatd'on the baseQihrnayfbe'lpositiohed substantially parano to the piuarlzd-se as 'idonea-dany screw 54 is then manually rotated until the arm 44 has reached the correct elevation at which time the thumb screw 52 is again tightened.

The enclosure 30 comprises a front wall 58, rear wall 60, and side walls 62 and 64 and a top Wall 66 which are secured together to form a chamber 68. A substantially vertical partition 70 extends across the lower portion of the enclosure 30 and divides the chamber 68 into two compartments 72 and 74. One of the compartments 72 contains the lamp 40 which is secured to a shelf 76 while the other compartment 74 contains the mounting member 26 which is rigidly secured to the base 28 and projects upwardly therefrom.

The mounting member 26 has a recess 76 formed in one side thereof that supports the lower optical member 32 so that the optically at surface thereon is positioned on top. A plurality of parts 78 project upwardly from the recess to retain the optical member 32 in position. A hinge 82, of any suitable construction, may be secured to the mounting member 26 so as to rotatably support one end of an elongated lever 80. The other end of the lever 80 may be provided with a downwardly projected contact finger 84 which is adapted to engage any objects 50 that may be placed on the work surface`48 of the anvil 44. It should be noted that the accuracy of the comparator 20 is dependent upon the axis 86 of the hinge 82 remaining in a xed position at all times. Accordingly, a knife blade 88 'as shown in Figure 12 may be provided on the member 26 so as to engage a notch 90 on the under side of the lever 80. A plurality of leaf springs 92 may engage the lever 80 and retain it in position on the knife blade 88. Thus the lever 80 may pivot about the knife edge 88 and cause the interference pattern to move. If it is desired to cause the pattern to rotate the axis 86 of the hinge 82 may be inclined so that it will intersect the plane of at least one of the optically Hat surfaces at an oblique angle alpha.

The upper optical member 34 Which/is preferably transparent is rigidly secured in position in the lever 80 so that the optically flat surface 38 thereon faces down directly onto the lower optically flat surface 36. This will place the two optically at surfaces in juxtaposition and the application of the proper illumination will create a light interference pattern 42 between the two surfaces that comprises a series of Newtonian fringes 93 and 95 or lines of light and dark intensity. The sensitivity of the comparator 20 is a function of the angle at which the axis 86 of the hinge 82 intersects the plane of the surfaces 36 and 38. In the present instance the axis of rotation 86 is parallel to the plane of surface 38 and therefore the sensitivity will be a function of the angle alpha or the angle at which the axis 86 of the hinge 82 intersects the plane of surface 36. Therefore, it is desirable to provide means for varying this angle. This may be achieved by any suitable means such as moving the position of the axis 86 or changing the slope of one of the at surfaces 36 and 38. ln the present instance the lower optically at surface 36 is moved. The lower optical member 32 has a clamping ring 96 on the exterior thereof that ts snugly between the posts 78 in the recess 76 positioned in the side of the mounting member. A lever 98 projecting from the side of the ring 96 forms a handle to facilitate rotating the lower optical member 32. Since the optically flat surface 36 on the top of the lower member 32 is not parallel to the bottom. as the handle 98 is moved the member 32 will rotate about a line oblique to the optically at surface 36. This will be effective to vary the angle alpha of intersection of the axis 86 and accordingly ,v the sensitivity of the comparator 20. The spacing of the fringes 93 and 95 is an index of the comparators sensitivity. Therefore, by providing a plurality of parallel spaced lines 100 on one of the optical members 34, it is possible to readily determine the correct spacing of the fringes 93 and 95 and thereby insure the correct sensitivity.

In order to produce a light interference pattern 42 having clearly defined fringe lines 93 and 95, it is advantageous to utilize a source of substantially monochromatic light such as helium or sodium vapor lamp 40. In order to minimize the etects of parallax, it is preferable that the interference pattern be created by light rays which enter the optical members 32 and 34 form as nearly normal to the optically flat surfaces 36 and 38 as possible and that the pattern 42 be observed from a direction as nearly normal to the surfaces 36 and 38 as possible. The light may be placed off center from the optical members 32 and 34, in which case a suitable refracting means is positioned above the optical members. A piece of opal glass 102 which bends light passing therethrough at right angles may be mounted between the upper end of the partition 70 and the upper edge of the front wall 58 to bend the light vertically down onto the optical members.

The Newtonian fringe 93 and 95 in the interference pattern are a result of the phase relationship of the light reflected from each of the optically at surfaces 36 and 38. The dark lines are the result of destructive interference and they occur where the distance between the optically flat surfaces 36 and 38 is an odd multiple of one quarter of the wave length of the light involved. The bright lines 93 result from the light reected from the two surfaces 36 and 38 being in phase and reinforcing each other. This occurs where the distance between the two surfaces is some multiple of one half of the wave length of the light involved. Since the surfaces '36 and 38 are optically Hat, rays of light striking the surface in parallel relation will leave the surface in parallel relation. Therefore the surfaces are substantially planar and the light and dark lines 93 and 95 will be straight and parallel with each other. The fringes 93 and 95 will also be parallel with the line of intersection of the planes containing the two optically at surfaces 36 and 38. As previously pointed out the axis of rotation 86 of the hinge 82 is oblique to at least one of the planes of the optical surfaces. Thus, as one of the members 32 or 34 pivots about this axis 86, thedirection of the line of intersection will appear to rotate.

A viewing system is provided so that the pattern 42v will always be observed from substantially the same direction which is preferably normal to the optically flat surfaces 32 and 34. The viewing system comprises a conventionalA telescope which is mounted in a horizontal position on the front wall 58 by means of a bracket 112. The telescope 110 is aimed at a small mirror 114 positioned on theback of the opal glass 102 and is focused on the interference pattern 42. The telescope 110 is provided with two independent cross-hairs 116 and 118 which are mounted between the objective 120 and pupilary lenses 122. The first cross-hair 116 is mounted to rotate with the ange 124 which projects radially from the barrel 126 of the telescope 110. The second cross-hair 118 is carried by the eye piece 130. By providing a scale 132 on the liange 124 and a pointer 134 on the eye piece 130, the relative position of the cross-hairs 116 and 118 may readily be ascertained. Thus, by separately aligning the cross-hairs with the fringes 93 and 95 before and after movement of the pattern 42, it is possible to determine the amount of rotational displacement of the pattern 42.

To make a comparison by means of the optical comparator 20, a standard 50 of known dimension is placed on the work surface 48 of the anvil 44. The crank 56 on the end of the screw 54 is then rotated so as to raise the anvil 44. This is continued until the standard 50 engages and lifts the contact finger 84. The comparator 20 is then calibrated to insure that the optical members 32 and 34 are correctly positioned for making a comparison by rs't adjusting the height of the anvil 44. As the anvil 44 causes the lever 80 Ato rise and fall, the direction of the fringes 93 and 95will rotate. This adjustment is continued until the lines run as parallel as possible to the three lines 100 on the surface of the optical member 3,4. After. the .frinseshave been` line-durf with the lines haben. the opticall members, the, anale.- alpha is adjusted to vary the spacing of the fringesA 95, and. 95 untilav designated` number appears between. thethree lines 1,005. In the. present.. instance this has arbitrarily been shown as fouij fringes. As previously stated, by turning theleyer- 98 toy rotatethe lower optical member 3 2, the direction ofthe slope can beeifectively controlled. This will resnlt inthe angle alphar at which, the axis $6. of the hinge 32 strikes,tlheplaney ofthe `surface 36 to chang?. Thiswigll varyxthespacing o f the. fringes 93 andy 95 and thus. thegsensitivityfof.thecomparator'20. Itshould be noted that; since the eiectiveelcvation, ofi the lowen optical member. 321` will change as ityisrotated, theheight of the anvil 44 should be" continuously adjusted during the, calibration. operation. to. maintain, the .fringes substantially. parallel to. thev lines 100 at. allmtirnes. After the. ..QmuaratonZit-bachecaadiustcdm progeny position thefringes.withrespeet tothe .lines,.th.1 anvil, `4:4 ialoclicd inplace. by, tightening, the thumb. screw 52... Although the direction; of, the fringesq. and.95 is` altered., by moving the anvil 44.- 1112.01", down,` it. mayN be diicult. t0v Place them. preciselyparallelto, the three,l lineslllO.` on the. optical flats. It, therefore desirable-,tofmale theange. 12,4 and cross-hair 115 adjustablel to allow an accurate and reliable indexingof` the position of. thefringes when the standard; piece.v t) is inthe comparator. 20,. After. the harige. has. been.. adjusted. to place. the. Cross-.hair 1.16 parallel. to thel fringes 93... and. 9.5.5l the, standjardrpiece is remos/edf from. under the. contaccnger 84. thus; allowing the lever 80 to rest on the stop 140. The objectr 50 of un know/n..size.is nextplacedon. the worklv surface 48 in ,engagement withfthe Contact. fingerr 8.4. If. the. dimension of. the object 50 differs from that of the` standard, the Contact linger S4 willv be in adifferentelevation.k This ini.. turn will cause the lever 80 to raise or lower` the upper: optical@ member 3.4: and change, theV direction. of. the interferencepattern 4K2. After the piece 5,0,.under exami- Ilouis. properly placed,vtheeyepiece. 1.3.0 of the telescope 11.0y is, rotated untilv the, cross-hairr 11,8; thereon is lined upI with; the new direction. ofthe fringes 9.3., and 95. Tzheangef124rernains stationary@duringl thisoperation. The pointer 134 which rotates. with; the `eyepiece 1h30 will then indicatei the amountl of relative. rotation of the fringe patternAZ. The scale-132.o,n the flange 124 may, he1 calibrated to read in ydegrees orydirectly. in.micro inches. lf the scale 132` is graduatedl in degrees; the difference between. the standard and the.unknown,.piece mayreadilybe calculated. It is4 apparentthat this .comparator Ztlmay. be employed for making.; precise comparisons. although it is particularly adapted .forl inspection worin where*v itis, necessary. to, repeatedly. measure objects osubstantially'the same dimensions. Once thecomparatoi- ,v 2 0 has been-properly. adjusted,iany. number ofv objects may befcornparedt with the original. standard without. the neessity of further adjustment.. However, it. may.y be desirable to occasionallyv insert` the standard piece to insure that the. comparator 20. is not out ofy adjustment.

For anunderstanding of how to calculate the size of theunlsnown. piece 50, reference may be h`ad,.toA Figure 2.which .is `a diagrammatic View of the air space between thelower and Iupper optically at surfaces'36 and- 38. As azmatter of convenience, this space maybe considered asbcing comprised of upper 142 and lower 144` wedges of: air. The upper wedge 142 is formedy between the lower surface 38 of the upper optical member` 3,4.Y and a h origontalreferenee plane 1.46. The bottom wedge 144 isfformedbetween theupper surface 36 of the lower optic aL member 32. andthe samev reference plane 146. The reference,Y plane `Mais defined by two lines, the axis 86 of` "i hingeland aline 14S Whichis perpendicular. to the ax1s86 andntersectsit, andv which is` also. parallel tothe top, surface. 3.6 of. thebottorn. optical flat.l member 3.2... The angle. alphaisf the. angie between theyre-.ference glane; 14.6 andthe topY surface 3.6 of the .bottom member theta. .(.Figure 3 ).r is 'the angle. at. which.. the frings, 93. and

9,5 strike the edge, of theflat and. isy determined. by the angles alpha and phi of the two air wedges,142.and,1.44.

'11o :calculate: the. dimension.. of.. the unknown piece. 50, the. following.enuationsapplyr wherex=vertical space between fringes (Figure 3), where )is-:horizontal lspace between fringes. Assuming that the optical members are square and have sides of lengthxL andthe was/,o ,lengthA of thelight is represented ,by A.

where-Ai is, the number of fringes per inch. (,In. the present embodimentythiswas setat 4f during calibration.) Therefore,

and the'. difference in the dimension between. the standard and unknown object is where B' isithe distance fronrthek hingeaxis to thecontact. finger.

While the foregoing description and figures have been connedto one embodiment, it will be apparent to those skilled in the art that numerous modifications may be made without departing from the. spirit thereof. Accordinglyit is to beunderstood that the foregoing is/to be considered as illustrative only and in no way restrictive, reference being hadto the appended claims to determine the .scope of the invention.

What isclaimedy is:

l.. In an optical comparator the combination of'a member having a substantially, optically flat-.surface thereon, and a second member havinga substantially optically ilat surface thereon which is in juxtaposition to saidfrst optically flat surface, pivot means supporting said second member for movement about an .axis of rotation, said axis being disposed obliquely to at leastone of said optically hat surfaces.

2. In `an optical'comparator the combination of a mcm ber having a substantially optically at surface thereon, a second member having a substantially optically flat surface thereon which is in juxtaposition to said first opticallyat surface, hinge means supporting one ofl said members for rotationabout an axiswhich is oblique to. the plane ofat least one of saidsurfaces, and a source of 'light positioned adjacent said members and Ailluminating rsaid optically at surfaces `and creating a light interference patternitherebetween.

3,@ Inan optical comparator the combination of'a stationary structure., a first member seatedon-said structure AVD and having a substantially optically at surface thereon, a second member having a substantially optically flat surface thereon in juxtaposition to said first optically flat surface, a source of substantially monochromatic light positioned adjacent said members and illuminating said optically fiat surfaces to thereby create a. light interference pattern therebetween, and hinge means secured to said stationary structure and carrying said sec-ond member, the axis of rotation of said hinge being oblique to one of said` surfaces whereby rotation of said second member about said axis will cause said interference pattern to appear to rotate.

4. In an optical comparator the combination of a stationary structure, a first member seated on said structure and having a substantially optically flat surface thereon, a second member having a substantially optically fiat surface thereon in juxtaposition to said first optically flat surface, a source of substantially monochromatic light positioned adjacent said members and illuminating said optically fiat surfaces to thereby create a light interference pattern therebetween, hinge means secured to said second member, said hinge means having an axis of rotation intersecting the plane of one of said optically fiat surfaces at an oblique angle, and adjusting means for varying the angle at which said axis intersects said optically fiat surface.

5. In an optical comparator the combination of a stationary structure, a first member seated on said structure and having a substantially optically flat surface thereon, a second member having a substantially optically fiat surface thereon in juxtaposition to said first optically fiat surface, a source of substantially monochromatic light positioned adjacent said members and illuminating said optically fiat surfaces to thereby create a light interference pattern therebetween, hinge means secured to said second member, said hinge means having an axis of rotation intersecting the plane of one of said optically at surfaces at an oblique angle, and means for rotating one of said members about said axis oblique to the optically fiat surface on said member to thereby vary the angle at which said axis intersects said optically fiat surface,

6. In an optical comparator the combination of a stationary structure, a first member having a base thereon seated on said structure, said member having a substantially optically at surface thereon inclined to said base, a second member having a substantially optically flat surface thereon in juxtaposition to said first optically fiat surface, a source of substantially monochromatic light positioned adjacent said members and illuminating said optically fiat surfaces and creating a light interference pattern therebetween, hinge means secured to said stationary structure and rotatably supporting said second member, said hinge means having an axis of rotation intersecting the plane of said first optically flat surface at an oblique angle, and means for rotating said first member about an axis substantially normal to said base to thereby vary the angle between the axis of said hinge and said plane.

7. In an optical comparator the combination of a stationary structure, a first member seated on said stationary structure and having a substantially optically flat surface thereon, a hinge on said stationary structure, a lever having one end thereof supported by said hinge, a second member carried by said lever and having an optically flat surface thereon in juxtaposition to said first surface, said hinge having an axis of rotation which is positioned oblique to the plane of one of said optically flat surfaces.

8. In an optical comparator the combination of a stationary structure, a first member seated on said stationary structure and having a substantially optically fiat surface thereon, a hinge on said stationary structure, a lever having one end thereof supported by said hinge, a second member carried by said lever and having an optically flat surface thereon in juxtaposition to said first surface, said hinge having an axis of rotation which is positioned to intersect the plane of one of said optically flat surfaces at an oblique angle, and means associated with one of said members for varying the angle at which said axis intersects said plane.

9. In an optical comparator the combination of a stationary sctructure, a first member seated on said stationary structure and having a. substantially optically flat surface thereon, a hinge on said stationary structure, a lever having one end thereof supported by said hinge, a second member carried by said lever and having an optically at surface thereon in juxtaposition to said first surface, said hinge having an axis of rotation which is positioned to intersect the plane of one of said optically fiat surfaces at an oblique angle, and means for rotating one of said members about an axis oblique to the optically flat surface on said member.

10. In an optical comparator the combination of a stationary structure, a first member seated on said stationary structure and having an optically flat surface thereon, means for rotating said first member about an axis oblique to said optically fiat surface, a hinge on said stationary structure, a lever having one end thereof supported by said hinge, a member carried by said lever and having an optically flat surface thereon in juxtaposition to said first optically at surface, and a source of light positioned adjacent said members and illuminating said `optically fiat surfaces to create a light interference pattern therebetween, said hinge having an axis of rotation positioned to intersect the plane of one of said optically fiat surfaces at an oblique angle whereby rotation of said lever will cause said interference pattern to appear to rotate.

l1. In an optical comparator the combination of a stationary structure, a first member seated on said stationary structure and having an optically flat surface thereon, means for rotating said first member about an axis oblique to said optically fiat surface, a hinge on said stationary structure, a lever having one end thereof supported by said hinge, a member carried by said lever and having an optically flat surface thereon in juxtaposition to said first optically at surface, a source of substantially monochromatic light positioned adjacent said members and illuminating said optically flat surfaces to create a light interference pattern therebetween, said hinge having an axis of rotation positioned to intersect the plane of one of said optically flat surfaces at an oblique angle whereby rotation of said lever will cause said interference pattern to appear to rotate, and means to measure the amount of said rotation.

12. In a gauge for comparing a dimension of an object with that of a standard of known size, the combination of a stationary structure having a work surface thereon adapted to support said object and said standard, a member supported by said stationary structure and having an optically flat surface thereon, a hinge supported by said stationary structure, a lever having a contact element adjacent one end thereof which is adapted to engage said object and said standard when they are positioned on said work surface, the opposite end of said lever being supported by said hinge, a second member carried by said lever and having an optically flat surface lthereon adjacent and directly opposed to said first optically flat surface, said hinge having an axis oblique to at least one of said optically at surfaces, and a source of light positioned adjacent said members to illuminate said optically flat surfaces and thereby create a light interference pattern therebetween.

13. In a gauge for comparing a dimension of an object with that of a standard of known size, the combination of a stationary structure having a work surface thereon adapted to support said object and said standard, a member supported by said stationary structure and having an optically fiat surface thereon, a hinge supported by said stationary structure, a lever having a contact element adjacent one end thereof adapted to engage said object and said standard when they are positionefl on said work surface, the opposite end of said lever being supported by said hinge, a second member carried by said lever and having an optically flat surface thereon in juxtaposition to said first optically at surface, and a source of substantially monochromatic light positioned adjacent said members to illuminate said optically flat surfaces and thereby create a light interference pattern therebetween, said hinge having an axis of rotation which is oblique to one of said optically at surfaces, whereby displacement of said contact element will cause said interference pattern to appear to rotate, and means for observing the amount of rotation of said interference pattern.

14. In a gauge for comparing a dimension of an object with that of a standard of known size, the combination of a stationary frame, a worksurface supported by said frame and adapted to carry said object and said standard, a member supported by said stationary frame and having an optically flat surface thereon, a hinge supported by said stationary frame, a lever having a contact element adjacent one end thereof adapted to engage said object and said standard when they are positioned on said work surface, the opposite end of said lever being supported by said hinge, a second member carried by said lever and having an optically flat surface thereon adjacent and directly opposed to said rst optically at surface, said hinge having an axis oblique to at least one of said surfaces, a source of substantially monochromatic light positioned adjacent said members to illuminate said optically flat surfaces and thereby create a light interference pattern therebetween.

15. ln a gauge for comparing a dimension of an object with that of a standard of known size, the combination of a stationary structure having a work surface thereon adapted to support said object and said standard, a member supported by said stationary structure and having an optically flat surface thereon, a hinge supported by said stationary structure, a lever having a contact element adjacent one end thereof adapted to engage said object and said standard when they are positioned on said work surface, the opposite end of said lever being supported by said hinge, a second member carried by said lever and having an optically flat surface thereon in juxtaposition to said first optically flat surface, a source of substantially monochromatic light positioned adjacent said members to illuminate said optically flat surfaces, and thereby create a light interference pattern, said hinge having an axis of rotation which intersects the plane of one of said optically ilat surfaces at an oblique angle whereby displacement of said contact element a distance corresponding to the difference between said standard and said object will cause said interference pattern to appear to rotate, means for rotating one of said optically flat surfaces about a line oblique to the optically at surface on said member to thereby vary the angle at which said axis intersects the plane of said surface, and means for observing the amount of rotation of said pattern.

16. In an optical comparator the combination of a lrst member having a substantially optically at surface thereon, a second member having a substantially optically fiat surface thereon which is adjacent and directly opposed to said first optically at surface, and a source of light positioned adjacent said members and creating a light interference pattern therebetween, at least one of said members being movably supported by a mounting means that positions said surfaces relative to each other so that relative movement therebetween will cause said light interference pattern to appear to rotate.

17. In an optical comparator the combination of a member having a substantially optically at surface thereon, a second member having a substantially opti- Gally dat surface thereon which is adjacent and directly opposed to said first optically at surface, a source of light positioned adjacent said members thereby illuminating said optically at surfaces and creating a light interference pattern therebetween and mounting means movably supporting at least one of said members to position said surfaces to each other so that relative movement therebetween will cause said interference pattern to appear to rotate.

18. ln a gauge for comparing a dimension of an object with that of a standard of known size, the combination of a stationary frame structure, a member positioned on said frame structure and having an optically flat surface thereon, a work platform adjustably mounted on said frame structure for supporting said object and said standard, a lever having a contact element adjacent one end thereof adapted to engage said object and said standard when they are positioned on said work platform, a hinge disposed on said frame structure and supporting the other end of said lever for pivoting about the axis of said hinge, a second member carried by said lever and having an optically fiat surface thereon adjacent and directly opposed to said tirst optically dat surface, at least one of said surfaces being oblique to said axis, and a source of light positioned adjacent said members to illuminate said optically at surfaces and thereby creating a light interference pattern therebetween.

19. In a gauge for comparing a dimension of an object with that of a standard of known size, the combination of a stationary frame structure, an arm adjustably supported on said frame, said arm having a work surface thereon adapted to support said object and said standard, a member positioned on said frame structure and having an optically flat surface thereon, a lever having a contact element adjacent one end thereof adapted to engage said object and said standard when they are positioned on said work surface, a hinge disposed on said frame structure and supporting the other end of said lever for pivoting about the axis of said hinge, said work surface being adjustable with respect to the axis of said hinge, a second member carried by said lever and having an optically flat surface thereon which is adjacent and directly opposed to said first optically at surface, and a source of light positioned adjacent said members to illuminate said optically flat surfaces and thereby create a light interference pattern therebetween, said member being mounted so that movement of said members about said axis will cause rotation of said pattern.

20. In a gauge for comparing a dimension of an object with that of a standard of known size, the combination of a stationary frame structure, an arm threadably supported on said frame, said arm having a work surface thereon adapted to support said object and said standard, a member positioned on said frame structure and having an optically flat surface thereon, a hinge disposed on said frame structure, a lever having a contact element adjacent one end thereof adapted to engage said object and said standard when they are positioned on said work surface, a second member carried by said lever and having an optically flat surface thereon adjacent and directly opposed to said first optically at surface, and a source of substantially monochromatic light positioned adjacent said members to illuminate said optically flat surfaces and thereby create a light interference pattern therebetween, at least one of said surfaces being oblique to said axis.

References Cited in the iile of this patent UNITED STATES PATENTS 1,824,153 Jacobs Sept. 22, 1931 2,450,839 Merritt Oct. 5, 1948 2,466,322 Merritt Apr. 5, 1949 

